The present invention relates to pneumatic stirring operations of a bath of molten metal by injecting a gas under the surface of the bath.
As is known, such operations are applicable to various industrial sectors and especially in siderurgy, in which it has already been proposed (French Pat. No. 2,322,202) to combine a pneumatic conversion process of cast iron into steel in a converter by blowing oxygen from above by means of a lance onto the bath of molten metal, with the blowing of an inert gas into the bath during and after the refining by oxygen through injection means communicating with the bath under the surface thereof and located in the wall of the converter, or usually in the bottom of the latter.
A handicap of this technique is that quite often the pneumatic stirring is only temporarily used or required for the treatment of the metal, while the injection of the gas, which produces the stirring is permanently required to prevent the molten metal from plugging up the means for the injection of the gas by solidifying at these means.
In this respect, if, taking under consideration the available pressure of the installation, the injection means is calibrated in such a manner as to obtain an optimal gas discharge during the stirring period, the minimum discharge necessary outside the stirring periods to protect the injection means against the risk of blocking, constitutes a substantial penalty to the economy of the arrangement, which cannot be justified for metallurgical reasons.
Conversely, if the injection means are calibrated in such a manner as to minimize the discharge of gas during the periods in which no stirring effect is required, it is often difficult, in fact impossible, to obtain the necessary gas throughput for an efficient stirring. While it may be possible to multiply the number of the injection means, in doing so, one would be back to the preceding problem.